Personally, I would most like a TV special that is entirely stand-alone with no references to anything else, so not even Yata hanging out with Zenigata, even though I really like him. I'd just really like to see something new and fresh.
I don't really like how Zenigata has been portrayed in the Koike movies, so I'm not that excited about a potential Zenigata-focused addition to that universe, but at the same time I'd like to see them wrap up the plot threads from the previous three. So if that's what's coming next, I'm game.